#include <iostream>
#include <cstdio>
using namespace std;
int n;
double ans,a,b;
int main()
{
    freopen("dog.in","r",stdin);
	freopen("dog.out","w",stdout);
	cin>>n;
	for(int i=1;i<=n;i++)
	{
		cin>>a>>b;
		b/=10;
		a*=b;
		ans+=a;
	}
	printf("%.2f",ans);
	fclose(stdin);
	fclose(stdout);
	return 0;
}
